Hydrophobic films and coatings, have garnered considerable attention in recent years due to a number of attractive qualities. Highly hydrophobic surfaces have been recognized in nature, perhaps most prevalently on lotus leaves and also on cicada wings. Because of its hydrophobic properties, the lotus leaf is capable of self-cleaning by the washing away of dust particles and debris as water droplets roll off its surface. This ability to self-clean is desirable in a number of modern-day applications.
To achieve these highly hydrophobic surfaces, hydrophobic particles have been added to the coatings and films to not only impart hydrophobicity, but also improve and/or enhance the mechanical properties of the coating or film.
One class of hydrophobic particles are hydrophobic silica or silica-like particles. Hydrophobic silica particles are generally prepared by first making silica particles either by pyrogenic or precipitation methods and then functionalizing the silica particles with appropriate hydrophobic groups, such as organosilicon or organohalogenosilane compounds. See for example, U.S. Pat. No. 3,677,784 (Nitzsche, et al.); U.S. Pat. No. 4,191,587 (Kratel et al.); and U.S. Pat. Publ. No. 2009/0298982 (Meyer et al.). Another method of making organically modified silica particles is disclosed by Arkhireeva et al. in J. Mater Chem., 2003, 13, 3122-3127, which discloses the synthesis of silsesquioxane nanoparticles using a sol-gel process. In this synthesis, sodium silicate, used as a seed, is combined with organotrialkoxysilane precursors to form silsesquioxane nanoparticles.